Vertebral body placement and method for spanning a space formed upon removal of a vertebral body

ABSTRACT

A vertebral body replacement includes first and second end plates, and a compliant connector section between the end plates having one or more helical cuts to provide limited compliance between the end plates. The compliant connector section can be provided in a separate spacer that fits between the end plates or directly in one or more of the end plates. The adjoining end plate surfaces, and/or adjoining surfaces of the spacer, include a rotational interlock to inhibit rotational motion between the surfaces and allow a modular stacking assembly of the vertebral body replacement to accommodate a wide range of patients.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to U.S.Provisional Application No. 60/981,665 filed Oct. 22, 2007, entitled“Method and Spacer Device Spanning Space Formed Upon Removal of anIntervertebral Disc,” the full disclosure of which is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to medical devices and methods. Morespecifically, the invention relates to vertebral body replacements andmethods of spanning a space formed upon removal of an intervertebraldisc.

Back pain takes an enormous toll on the health and productivity ofpeople around the world. According to the American Academy of OrthopedicSurgeons, approximately 80 percent of Americans will experience backpain at some time in their life. In the year 2000, approximately 26million visits were made to physicians' offices due to back problems inthe United States. On any one day, it is estimated that 5% of theworking population in America is disabled by back pain.

One common cause of back pain is injury, degeneration and/or dysfunctionof one or more intervertebral discs. Intervertebral discs are the softtissue structures located between each of the thirty-three vertebralbones that make up the vertebral (spinal) column. Essentially, the discsallow the vertebrae to move relative to one another. The vertebralcolumn and discs are vital anatomical structures, in that they form acentral axis that supports the head and torso, allow for movement of theback, and protect the spinal cord, which passes through the vertebrae inproximity to the discs.

Another form of spinal injury involves injury or deformity of thevertebra themselves. When one or more vertebrae is fracture or deformedby tumor or other causes and results in pain and discomfort, surgery isoften required. Traditionally, surgical procedures for vertebralreplacement have involved removal of the vertebra and fusion of the twovertebrae above and below the missing vertebra. It is necessary toreplace the removed vertebra to maintain spacing of adjacent vertebrae.Oftentimes, pins, rods, screws, cages and/or the like are insertedbetween the vertebrae to act as support structures to hold the vertebraeand graft material in place while they permanently fuse together. Thesevertebral body replacement procedures generally focus on rigidly fusingthe adjacent vertebrae and preventing motion.

However, it would be desirable to achieve immobilization of thevertebrae adjacent a removed vertebral body and maintain spacing betweenthe adjacent vertebrae without the complete rigidity of traditionalinterbody fusion.

Another problem associated with the typical vertebral body replacementprocedure is the subsidence of the cage into the vertebral body. Thetypical vertebral body replacement cage is formed with a largepercentage of open space to allow the bone to grow through and form thebridging bone which immobilizes the vertebrae. However, the large amountof open space means that the load on each segment of the cage issignificantly higher than if the cage surface area was larger. Thisresults in the cage subsiding or sinking into the bone over time andallows the space between the vertebrae to collapse.

Therefore, a need exists for improved vertebral body replacement andmethod for spanning a space and maintaining spacing between twovertebrae after removal of an intervertebral body. Such improved methodand intervertebral body replacement would avoid the need for growth ofbridging bone between the remaining vertebrae.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention provide a vertebral bodyreplacement with compliance or shock absorption and methods of spanninga space formed upon removal of vertebral body.

In accordance with one of numerous aspects of the present invention, avertebral body replacement for replacing at least one vertebral bodybetween remaining upper and lower vertebral bodies, the vertebral bodyreplacement comprises a first end plate having an upper surfaceconfigured to engage against a surface of the upper remaining vertebralbody, and a lower surface opposite the upper surface spanning the firstend plate, a second end plate having a lower surface configured toengage against a surface of the lower remaining vertebral body, and acompliant connector section between the first end plate lower surfaceand the second end plate lower surface, the compliant connector sectioncomprising at least one helical cut configured and arranged to permitlimited motion between the first end plate and the second end plate.

In accordance with another aspect of the invention, a method ofreplacing at least one vertebral body comprises removing said at leastone vertebral body between two remaining vertebral bodies, placing avertebral body replacement between said two remaining vertebral bodies,the vertebral body replacement comprising first and second end platesand a compliant connector section between the first and second endplates, the compliant connector section having at least one helical cutand configured and arranged to limit motion to less than 10 degreesbetween said remaining vertebral bodies, and maintaining the spacebetween the two remaining vertebral bodies with the vertebral bodyreplacement.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a vertebral body replacement accordingto one embodiment of the present invention;

FIG. 1A is an exploded, perspective view of the vertebral bodyreplacement of FIG. 1;

FIG. 2 is a perspective view of a vertebral body replacement accordingto a second exemplary embodiment of the present invention; and

FIG. 3 is a perspective view of a vertebral body replacement accordingto a third exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Various embodiments of the present invention generally provide for avertebral body replacement having upper and lower plates or surfacesconnected by a central connector portion which provides some limitedamount of axial compliance and/or rotational motion between the upperand lower plates or surfaces. The compliant vertebral body replacementaccording to the present invention can maintain disc height and preventsubsidence with a large surface area while improving outcomes byallowing some limited motion and providing improved fixation. Thecompliance of the vertebral body replacement also functions to reduceloading on the interface between the bone and vertebral bodyreplacement.

One example of a vertebral body replacement 10 for replacement of avertebral body and maintaining disc height between two adjacentvertebral discs is shown in FIG. 1. The body 10 includes at least oneend plate 20 having a vertebral body contacting surface 24, a second endplate or body end 30 opposite the end plate 20, and a compliantconnector or connector section 32 interposed between, orinterconnecting, the two ends 20, 30. As will be described below, somelimited rotational and axial motion may be provided between the twoplates or sections 20, 30 to reduce loading on the interface between theadjacent vertebral bodies and the body 10. According to an exemplarydevice embodying principles of the present invention, the compliance ofthe connector 32, as well as some small amount of translation androtation, is provided by lateral cuts or slots 70 extending into theconnector 32. The body 10 when implanted between two vertebrae maintainsa desirable space between the two adjacent vertebrae similar to thatprovided by a natural vertebra.

Although the body 10 has been shown as generally oblong in crosssection, other shapes may be used, including circular, oval, elliptical,or rectangular. Although the connector section 32 has been illustratedin FIG. 1 as integral with the end section 30, according to otherembodiments, the connector can include one or more separate compliantconnectors or spacers in other configurations and at other locations. Byway of example, a compliant connector may be the same or substantiallythe same diameter, size, and shape as the plates, multiple connectorscan be arranged in a rectangular pattern, or a hollow cylindricalconnector can be used. Further optionally, while the surfaces 24 areillustrated being perpendicular to the vertical axis of the body 10, oneor both of the surfaces 24 can be somewhat wedge-shaped, formed with oneor two lordosis angles, as well known to those of ordinary skill in theart. The modular design of the upper plate 20 and the lower platesection 30 allows the creation of a complete bodies 10 of differentsizes to correspond to the particular space for each patient.

The upper plate 20 and the lower plate or plate section 30, andconnector 32, may be constructed from any suitable metal, alloy orcombination of metals or alloys, such as but not limited to cobaltchrome alloys, titanium (such as grade 5 titanium), titanium basedalloys, tantalum, nickel titanium alloys, stainless steel, and/or thelike. They may also be formed of ceramics, biologically compatiblepolymers including PEEK, UHMWPE (ultra high molecular weightpolyethylene) or fiber reinforced polymers. However, when polymer isused for the body 10, the contacting surfaces 24 may be coated orotherwise covered with metal for fixation. The upper plate 20 and thelower plate or plate section 30, and connector 32, may be formed of aone piece construction or may be formed of more than one piece, such asdifferent materials coupled together. When the body 10 is formed ofmultiple materials, these materials are fixed together to form a unitaryone piece spacer without separately moving parts.

Different materials may be used for different parts of the body 10 tooptimize imaging characteristics. For example, the upper plate 20 andthe lower plate or plate section 30 may be formed of titanium, while theconnector 32 is formed of cobalt chromium alloy for improved imaging ofthe plates. Cobalt chrome molybdenum alloys, when used for the plates20, 30 may be treated with aluminum oxide blasting followed by atitanium plasma spray to improve bone integration. Other materials andcoatings can also be used such as titanium coated with titanium nitride,aluminum oxide blasting, HA (hydroxylapatite) coating, micro HA coating,and/or bone integration promoting coatings. Any other suitable metals orcombinations of metals may be used as well as ceramic or polymermaterials, and combinations thereof. Any suitable technique may be usedto couple materials together, such as snap fitting, slip fitting,lamination, interference fitting, use of adhesives, welding and/or thelike.

In some embodiments, the outer surface 24 is planar. Oftentimes, theouter surface 24 will include one or more surface features and/ormaterials to enhance attachment of the body 10 to vertebral bone. Forexample, as shown in FIG. 1, the outer surface 24 may be machined tohave serrations 40 or other surface features for promoting adhesion ofthe plates 20, 30 to a vertebra. In the embodiment shown, the serrations40 are pyramid shaped serrations extending in mutually orthogonaldirections, but other geometries such as teeth, grooves, ridges, pins,barbs or the like would also be useful. When the bone integrationstructures are ridges, teeth, barbs or similar structures, they may beangled to ease insertion and prevent migration. These bone integrationstructures can be used to precisely cut the bone during implantation tocause bleeding bone and encourage bone integration. Additionally, theouter surface 24 may be provided with a rough microfinish formed byblasting with aluminum oxide microparticles or the like to improve boneintegration. In some embodiments, the outer surface may also be titaniumplasma sprayed or HA coated to further enhance attachment of the outersurface 24 to vertebral bone.

The outer surfaces 24 may also carry one or more upstanding fins 50, 52which also extend laterally in an anterior-posterior direction. The fins50, 52 are configured to be placed in slots in the vertebral bodies.Preferably, the fins 50, 52 each have a height greater than a width andhave a lateral length greater than the height. In one embodiment, thefins 50, 52 are pierced by transverse holes 54 for bone ingrowth. Thetransverse holes 54 may be formed in any shape and may extend partiallyor all the way through the fins 50, 52. In alternative embodiments, thefins 50, 52 may be rotated away from the anterior-posterior axis, suchas in a lateral-lateral orientation, a posterolateral-anterolateralorientation, or the like.

The fins 50, 52 provide improved attachment to the bone and preventrotation of the plates 20, 30 in the bone. In some embodiments, the fins50, 52 may extend from the surface 24 at an angle other than 90°. Forexample, on one or more of the plates 20, 22 where multiple fins 52 areattached to the surface 24, the fins may be canted away from one anotherwith the bases slightly closer together than their edges at an anglesuch as about 80-88 degrees. The fins 50, 52 may have any other suitableconfiguration including various numbers angles and curvatures, invarious embodiments. In some embodiments, the fins 50, 52 may be omittedaltogether. The embodiment of FIG. 1 illustrates a combination of oneplate with a single fin 50 and another plate with a double fin 52. Thisarrangement is useful for double level disc replacements and utilizesoffset slots in the vertebral body to prevent the rare occurrence ofvertebral body splitting by avoiding cuts to the vertebral body in thesame plane for multi-level implants. The combination of the single fin50 and double fin 52 can also assist the surgeon in placement of thespacer in the correct orientation.

The body 10 has been shown with the fins 50, 52 as the primary fixationfeature; however, the fins may also be augmented or replaced with one ormore screws extending through the plates and into the bone. For examplein the body 10 of FIG. 1, the upper fin 50 may be augmented or replacedwith one or more screws (not illustrated) while the two lower fins 52remain. The plates 20, 30 can be provided with one or a series of holes60 to allow screws to be inserted at different locations at the optionof the surgeon. However, the holes 60 should not be of such size ornumber that the coverage of the plate 20, 30 is decreased to such anextent that subsidence occurs. Alternately, the screws can passlaterally through one or more of the holes in the fins. When one or morescrews are provided, they may incorporate a locking feature to preventthe screws from backing out. The screws may also be provided with a boneintegration coating.

Some limited holes may also be provided in the plate to allow boneingrowth. However, if the outer surfaces 24 have holes therein, theholes advantageously cover less than 40 percent of the outer surface 24which contacts the bone to prevent subsidence of the plates into thevertebral bodies. Preferably the holes will cover less than 25 percent,and more preferably less than 10 percent of the outer bone contactingsurfaces. At the option of the surgeon, when the small holes are presentin the plates 20, 30, bone graft can be placed in the holes to allowbone to grow through the plates. The embodiments illustrated in FIGS.1-3 also illustrate the optional inclusion of countersunk screw holes 60extending between a lateral surface of the plates 20, 30 and the endsurfaces 24, in which bone screws may optionally be inserted to furtherstabilize the body 10. The holes 60 can alternatively extend verticallythrough the end plates, or the end plates can include combinations ofvertical and angled holes.

The vertebral body replacement 10 shown herein is configured forplacement in the vertebral column from an anterior approach. It shouldbe understood that other approaches can be used, and the particularshape of the vertebral body replacement would be modified depending onthe approach. For example, for a lateral approach, the vertebral bodyreplacement may be formed in a more elongated, kidney bean, or bananashape with a transversely oriented fin.

As shown in FIG. 1, the vertebral body replacement 10 is provided withshock absorption or some other limited motion between the two plates 20,30 by providing a compliant connector 32. The limited motion provided bythe compliant connector 32 is designed to reduce forces on the interfacebetween the outer surfaces 24 and the bone to improve long term fixationof the spacer. The compliance of the connector 32 allows motion betweenthe vertebral bodies to be accommodated by the compliance in the body 10rather than causing one or both of the vertebral bodies to pull awayfrom the plates 20, 30. The compliant connector 32 provides limitedrelative motion between the plates, which may include compliance in avertical direction of up to about 6 mm, rotation in ananterior/posterior direction, lateral direction, or axial rotation ofless than about 10 degrees, and/or translation of up to about 1 mm.

In the vertebral body replacement 10 of FIG. 1, the compliance, as wellas some small amount of translation and rotation, is provided by thecuts or slots 70 extending into the connector 32. In the embodiment ofFIG. 1, the slots 70 are spiral slots, however, other shaped slots mayalso be used. The compliant connector 32 is advantageously formed as aunitary member with at least one lateral cut or slot 70 positionedbetween the upper and lower plates 20, 30, permitting the plates to moveresiliently toward and away from each other. The replacement 10 can alsobe formed as multiple parts where different properties are desired fromthe different parts, such as different radiopacities, differentstrengths, or different flexibility properties and for flexibility increating the size and configuration of spacer suited to the patient. Thelateral cuts 70 in the connector 32 allow the connector to function as acompliant member without affecting the function of the upper and lowerplates of the body 10.

FIG. 2 illustrates an alternative embodiment of a body 10 havingmultiple parts including end plates 20, 30 and spacers 90. The spacers90 include lateral cuts 70 in place of the spiral cuts of FIG. 1. Thematerial remaining after the cuts 70 are made is called a column. Ashallow cut, that is, one that extends laterally into the connector arelatively small distance, and a large column provides a stiffer spacer,while a deeper cut and smaller column provides a more compliant spacer.In the embodiment shown in FIG. 2, the cuts 70 are at least 60% of theway through the spacer width or diameter, and preferably at least 75% ofthe way through the connector width.

Optionally, a variable stiffness shock absorbing connector 32 (FIG. 1)or spacer 90 (FIG. 2) can be constructed with lateral cuts 70 withtapering widths. For cuts with such tapering widths, the cut 70 issmallest where the cut terminates adjacent the column and is largest atthe edge of the connector 32 furthest from the column. In this version,each of the lateral cuts 70 causes the connector 32 to act as a nonlinear spring providing progressively stiffer behavior upon largercompression. This is due to the fact that progressively more material onthe sides of the cuts 70 is in contact as the connector 32 or spacer 90is compressed. The non-linear spring can be incorporated in any of theother embodiments described herein to provide a softer stop to thecompliant action of the core. The tapered width cuts 70 can provide theadditional benefit of providing a flushing action during operation thatmoves any accumulated material out of the cuts.

The cuts 70 also advantageously include a stress relief 74 at the end ofthe cuts which increases the fatigue life of the device by reducing thestress concentration at the ends of the slots.

In the exemplary embodiments illustrated herein, a shock absorbingconnector 32 includes either one or more planar cuts 70 (FIG. 2), oralternatively one or more spiral or helical cuts 70 (FIG. 1) to form oneor more continuous spring coil elements 72 which provide compliance tothe connector. Although the spiral cut connector 32 is illustrated inFIG. 1 with two spiral cuts, only one, or three or more spiral cuts mayalso be employed. For example, two or more spiral cuts 70 arranged inopposite directions can be formed in the connector 32, as illustrated inFIG. 1. Furthermore, when more than one spiral cut 70 is provided, thecuts can optionally be nested one inside the other (not illustrated), asin the manner of a multi-start thread, and/or can include combinationsof both nested and adjacent cuts (such as those illustrated in FIGS.1-2). The compression of a spiral cut connector 70 can result in somesmall amount of relative rotation between the upper and lower surfaces20, 30. In cases where it is desirable to eliminate this rotation, aconnector 32 having multiple spiral cuts in opposite directions can beused. For example, a connector 32 can be formed with a first spiral cut70 at a top of the connector in a first direction and a second spiralcut 70 at a bottom of the core in an opposite second direction. Thefirst and second spiral cuts can offset rotation of each other resultingin a non rotating compliant connector. The double spiral embodiment ofthe connector is also more stable in shear than the single coil.Furthermore, coils 74 provide significantly more surface area betweenthe adjoining surfaces of the cuts 70 than do planar cuts, which can beadvantageous to allow limited rotational motion. The spiral cuts 70 canbe made parallel to the end surfaces of the body 10 or can be angled, asin a cone shape. When the spiral cuts 70 are angled to form a coneshaped spring the cone shaped surfaces can limit the translationalmovement of the spring.

In each of the shock absorbing connectors described herein, theinterconnected sections within the connector and the plate(s) aredesigned for minimal or no motion between contacting parts to preventparticulate generation. However, since the plates and connectors aremade entirely of hard materials such as metals, some minimal rubbingcontact may be accommodated. In the exemplary embodiments illustrated infigures herein, a rotational interlock 80 is provided between the lowersurface of the end plate 20 and the adjoining upper surface of theconnector section 32 of the end plate 30. With reference to FIG. 2, theexemplary interlock 80 includes complementary portions 82, 84, formed onthe adjoining faces of the end plate 20 and the connector section 32, inthe exemplary body 10, taking the shape of simple raised portions orribs 84 which mate with correspondingly sized and shaped recesses 82.The rotational interlock 80 is not limited to the particular shapes ororientations illustrated in the drawing figures, and can take any shapeor orientation which resists, and advantageously prevents, the plate 20and the connector section 32 from rotating relative to each other. Therotational interlock 80 on the top and bottom surface of a spacer 90 canbe different to allow the complete body 10 to be assembled only in aparticular desired configuration.

Further optionally, as illustrated in FIG. 1A, the body 10 can includeone or more blind cavities 86 extending vertically through the connectorsection 32, which provides the interior side of the spiral cut 70. Theblind cavities 86 can also vary in cross sectional size and shape totailor the rigidity of the connector section 32 in different directions.More specifically, the cavity or cavities 86, only one of which isillustrated in FIG. 1A, when left hollow, provides a less rigidconnector 32. To increase the rigidity of the connector section 32,other material can be used to partially or completely fill the cavity86, such as pins or rods (not illustrated) inserted in the cavity.

When implanted between vertebrae, the shock absorbing connector 32 canresiliently absorb shocks transmitted vertically between upper and lowervertebrae of the patient's spinal column. This shock absorption isrelated to the material properties, design, and dimensions of theconnector. In general, an increased number and width of the cuts 70 willincrease absorption of shocks, with more elastic, or springy compressionbetween the vertebrae.

Preferably the connector 32 is made of metal such as titanium, cobaltchromium alloy, stainless steel, tantalum, nickel titanium or acombination thereof. These materials also can be designed to provide adevice which is deformable in the elastic region of the stress/straincurve and will not plastically deform during compression.

In the embodiments illustrated herein, the number, pitch, lead, leadangle, handedness, and total vertical length of each of the spiral cutsor slots 70, as well as the combination of multiple cuts if provided,can be varied to change the amount of compliance of the connector 32.When a load is applied to the upper and lower plates 20, 30, theconnector 32 will compress with each of the cuts 70 closing and thetotal amount of compression possible depending on the number,arrangement, and height of the cuts. The cuts 70 form spiral coils 74between the ends of the cut, which function like springs to allow theconnector 32 to be compressed. The cuts 70 may be modified to benon-uniform to provide preferential deflection in one or more bendingdirections. Preferential deflection is useful to provide increasedanterior-posterior compliance and less lateral compliance, or the otherway around.

According to one embodiment of the invention, the cuts 70 in the shockabsorbing connector 32 according to any of the embodiments describedherein may be manufactured by wire EDM (electrical discharge machining),molding, laser cutting, or the like. A number of cuts 70 can vary from 1to about 50, preferably about 6 to about 20, for a vertebral bodyreplacement. A width of the lateral cuts 70 in the direction of theheight of the body 10 is about 0.01 mm to about 2 mm, preferably about0.05 to about 1 mm.

In one embodiment of the present invention, for a cervical application,the maximum deformation of the shock absorbing body is about 0.5 toabout 4 mm, and is preferably about 1 to about 2 mm. For a lumbarapplication, the maximum deformation of the shock absorbing body isabout 1 to about 6 mm, and is preferably about 1 to about 3 mm.

Although motion between the plates 20, 30 of the body 10 has beendescribed herein as provided by cuts 70, it should be understood thatthis motion can be provided in a number of other known manners, such asuse of resilient materials, or movable joints as long as the motion islimited to the small amount of motion allowable in a patient requiring afusion procedure including compliance or vertical motion between theplates of up to about 6 mm, rotation between the plates of less than 10degrees, and translation between the plates of up to about 1 mm.

The body 10 can be provided in different sizes, with different platesizes, angles between plates, lordosis angles, and heights for differentpatients or applications. In addition, the shock absorbing connectorsection 32 can be provided in different compliances for differentpatients. In addition, the compliance and/or height of the body 10 canbe adjustable, such as by rotating an adjustment screw before or afterimplantation, and/or bonding portions of one or more of the portions ofa coil 74. The body 10 preferably is sized to provide substantialcoverage of the vertebral surfaces. For example, in an anteriorprocedure, the plates 20, 30 are preferably sized to cover at least 50percent of the vertebral surface. In posterior or lateral procedures,the coverage of the vertebral surface may be somewhat smaller due to thesmall size of the access area, i.e., the posterior or lateral spacersmay cover about 40 percent or more of the vertebral surface with a oneor two part spacer.

Turning now to FIG. 2, a second exemplary embodiment of a body 10,adhering to principles of the present invention, is illustrated. Incontrast to the embodiment illustrated in FIGS. 1 and 1A, the body 10illustrated in FIG. 2 includes one or more separate compliant connectorspacers 90 positioned between plates 20, 30, rather than a connectorsection 32 of a plate 30. Each of the spacers 90 includes one or morecuts 70, which can be either planar cuts or forming one or more coils,as described above with reference to the embodiment of FIGS. 1 and 1A.The adjoining surfaces of the plates 20, 30 and the spacers 90 are alsoprovided with rotational interlocks 80, as described herein; while FIG.2 suggests that the interlocks 80 are the same, differently configuredinterlocks can alternatively be provided for different non-adjoiningsurfaces, for example to prevent the spacers 90 from being assembled ina way other than that designed for a body 10 configured for theparticular patient. By way of non-limiting example, a first rotationalinterlock, formed of rectangular ribs and recesses on adjoining surfacesof the end plates and/or the spacers, as illustrated in FIG. 1A, can beprovided on the adjoining surfaces of the plate 20 and the adjacentfirst spacer 90; a second rotational interlock, formed of verticallyoriented cylindrical pins, can be provided on the opposite face of thefirst spacer 90 and the adjoining surface of the adjacent spacer orplate 30. Because the two interlocks 80 are incompatible and do notmate, there is only a single configuration of the pieces that willpermit them to be assembled into a body 10.

FIG. 3 illustrates a third exemplary embodiment of a body 10, adheringto principles of the present invention. In addition to the featurespreviously described with reference to FIGS. 1-2, the embodimentillustrated in FIG. 3 includes a vertical adjustment mechanism 100 forfine tuning of the vertical size of the body 10, either prior to orafter implantation of body 10 into a patient. While numerousconfigurations of the adjustment mechanism 100 can be provided, oneexemplary embodiment includes a threaded post or tube 102 extending fromeither an upper surface 106 of the end plate 30 or a lower surface 104of the section 32, which mates with a correspondingly configured andthreaded hole or post in the other of the end plate 30 and section 32.Rotation of the post 102 causes the two portions of the body 10 to movetoward or away from each other, and thus decreases or increases thevertical size of the body 10, respectively. According to one version ofthe adjustable height vertebral body replacement an adjustment mechanismwith oppositely threaded ends is inserted in the upper and lower parts104, 106 and is adjustable after positioning in the patient.

According to one exemplary method adhering to principles of the presentinvention, a patient in need of a vertebral body replacement is preppedand surgical access is made to the particular vertebral body to beremoved. Access to the surgical site is generally made anteriorlythrough the abdominal cavity for a lumbar procedure. One or more targetvertebral body or bodies is removed in one of numerous manners known tothose of ordinary skill in the art, between upper and lower remainingvertebral bodies in the patient's spine, and a vertebral bodyreplacement 10, embodying principles of the present invention, isselected based on the measurement of the spacing for proper spinalalignment. The vertebral body replacement 10 is assembled and implantedin the space created by removal of the original vertebral body orbodies. Optionally, one or more spacers 90 are assembled into the body10, prior to installation of the body 10 into the patient, and/or thevertical length of the body 10 is adjusted to better fit in the space.Further optionally, when the body 10 includes one or more cavities 86,additional material is inserted into the cavity, prior to implantationof the body, to tailor the rigidity of the body 10, or for otherpurposes.

While the exemplary embodiments have been described in some detail, byway of example and for clarity of understanding, those of skill in theart will recognize that a variety of modifications, adaptations, andchanges may be employed. Hence, the scope of the present inventionshould be limited solely by the appended claims.

What is claimed is:
 1. A vertebral body replacement for replacing atleast one vertebral body between remaining upper and lower vertebralbodies, the vertebral body replacement comprising: a first end platehaving an upper surface configured to engage against a surface of theupper remaining vertebral body, and a lower surface opposite the uppersurface spanning the first end plate; a second end plate having a lowersurface configured to engage against a surface of the lower remainingvertebral body; a compliant connector section between the first endplate lower surface and the second end plate lower surface, thecompliant connector section comprising a plurality of separate stackablespacers each having at least one helical cut configured and arranged topermit limited rotation between the first end plate and the second endplate in an anterior/posterior direction and a lateral direction; and arotational interlock on the first end plate lower surface and an uppersurface of at least one of the spacers, the rotational interlock beingconfigured and arranged to inhibit rotational motion between the firstend plate lower surface and the at least one spacer upper surface,wherein the rotational interlock comprises a first raised elongateportion extending in the anterior/posterior direction or the lateraldirection on one of the first end plate lower surface or the at leastone spacer upper surface and a first complementary elongate recess inthe opposite surface.
 2. The vertebral body replacement of claim 1,wherein the second end plate includes an upper surface opposite thesecond end plate lower surface and spanning the second end plate, thecompliant connector section located between the second end plate lowerand upper surfaces.
 3. The vertebral body replacement of claim 2,wherein said rotational interlock is a first rotational interlock, andfurther comprising a second rotational interlock on the first end platelower surface and the second end plate upper surface, the secondrotational interlock configured and arranged to at least inhibitrotational motion between the first end plate lower surface and thesecond end plate upper surface.
 4. The vertebral body replacement ofclaim 1, wherein the compliant connector section is configured andarranged to limit motion to less than 10 degrees between said remainingvertebral bodies.
 5. The vertebral body replacement of claim 1, whereinthe at least one helical cut in each of the separate stackable spacersare oppositely oriented.
 6. The vertebral body replacement of claim 1,wherein said rotational interlock is a first rotational interlock,wherein the at least one spacer has a lower surface spanning the atleast one spacer, wherein the second end plate has an upper surfacespanning the second end plate, and further comprising: a secondrotational interlock on the second end plate upper surface and the atleast one spacer lower surface, the second rotational interlockconfigured and arranged to at least inhibit rotational motion betweenthe second end plate upper surface and the at least one spacer lowersurface, wherein the second rotational interlock comprises a secondraised elongate portion extending in the anterior/posterior direction orthe lateral direction on one of the second end plate upper surface orthe at least one spacer lower surface and a second complementaryelongate recess in the opposite surface.
 7. The vertebral bodyreplacement of claim 6, wherein the first and second rotationalinterlocks are different.
 8. The vertebral body replacement of claim 1,further comprising: an adjustment mechanism between the first and secondend plates, the adjustment mechanism configured and arranged toselectively move the first and second end plates towards and away fromeach other.
 9. The vertebral body replacement of claim 1, furthercomprising at least one bone ingrowth hole in at least one of the firstand second end plates.
 10. The vertebral body replacement of claim 1,wherein each of the first and second end plates comprise a lateralsurface, and wherein the at least one bone ingrowth hole extends betweensaid lateral surface and said surface configured to engage against asurface of a remaining vertebral body.
 11. The vertebral bodyreplacement of claim 1, wherein the vertebral body replacement is sizedand shaped to replace one or more entire vertebral bodies of the humanspine.
 12. A vertebral body replacement for replacing at least onevertebral body between remaining upper and lower vertebral bodies, thevertebral body replacement comprising: a first end plate having an uppersurface configured to engage against a surface of the upper remainingvertebral body, and a lower surface opposite the upper surface spanningthe first end plate; a second end plate having a lower surfaceconfigured to engage against a surface of the lower remaining vertebralbody; a compliant connector section between the first end plate lowersurface and the second end plate lower surface, the compliant connectorsection comprising a plurality of separate stackable spacers each havingat least one helical cut configured and arranged to form a continuousspring coil element; and a rotational interlock on the first end platelower surface and an upper surface of at least one of the spacers, therotational interlock being configured and arranged to inhibit rotationalmotion between the first end plate lower surface and the at least onespacer upper surface, wherein the rotational interlock comprises araised elongate portion extending in the anterior/posterior direction orthe lateral direction on one of the first end plate lower surface or theat least one spacer upper surface and a complementary elongate recess inthe opposite surface.
 13. The vertebral body replacement of claim 12,wherein the vertebral body replacement is sized and shaped to replaceone or more entire vertebral bodies of the human spine.
 14. A vertebralbody replacement for replacing at least one vertebral body betweenremaining upper and lower vertebral bodies, the vertebral bodyreplacement comprising: a first end plate having an upper surfaceconfigured to engage against a surface of the upper remaining vertebralbody, and a lower surface opposite the upper surface spanning the firstend plate; a second end plate having a lower surface configured toengage against a surface of the lower remaining vertebral body and anupper surface; a compliant connector section between the first end platelower surface and the second end plate lower surface, the compliantconnector section comprising a plurality of separate stackable spacerseach having at least one helical cut configured and arranged to form acontinuous spring coil element; and a rotational interlock on the secondend plate upper surface and a lower surface of at least one of thespacers, the rotational interlock being configured and arranged toinhibit rotational motion between the second end plate upper surface andthe at least one spacer lower surface, wherein the rotational interlockcomprises a raised elongate portion extending in the anterior/posteriordirection or the lateral direction on one of the second end plate uppersurface or the at least one spacer lower surface and a complementaryelongate recess in the opposite surface.
 15. The vertebral bodyreplacement of claim 14, wherein the vertebral body replacement is sizedand shaped to replace one or more entire vertebral bodies of the humanspine.
 16. A vertebral body replacement for replacing at least onevertebral body between remaining upper and lower vertebral bodies, thevertebral body replacement comprising: a first end plate having an uppersurface configured to engage against a surface of the upper remainingvertebral body, and a lower surface opposite the upper surface spanningthe first end plate; a second end plate having a lower surfaceconfigured to engage against a surface of the lower remaining vertebralbody and an upper surface opposite the lower surface and spanning thesecond end plate; a compliant connector section between the first endplate lower surface and the second end plate lower surface, thecompliant connector section comprising a plurality of separate stackablespacers each having at least one helical cut configured and arranged topermit limited rotation between the first end plate and the second endplate in an anterior/posterior direction and a lateral direction; and arotational interlock on the second end plate upper surface and a lowersurface of at least one of the spacers, the rotational interlock beingconfigured and arranged to inhibit rotational motion between the secondend plate upper surface and the at least one spacer lower surface,wherein the rotational interlock comprises a raised elongate portionextending in the anterior/posterior direction or the lateral directionon one of the second end plate upper surface or the at least one spacerlower surface and a complementary elongate recess in the oppositesurface.
 17. The vertebral body replacement of claim 16, wherein thecompliant connector section is located between the second end platelower and upper surfaces.
 18. The vertebral body replacement of claim16, wherein the compliant connector section is configured and arrangedto limit motion to less than 10 degrees between said remaining vertebralbodies.
 19. The vertebral body replacement of claim 16, wherein the atleast one helical cut in each of the separate stackable spacers areoppositely oriented.
 20. The vertebral body replacement of claim 16,wherein said rotational interlock is a first rotational interlock, andfurther comprising a second rotational interlock on the first end platelower surface and the second end plate upper surface, the secondrotational interlock configured and arranged to at least inhibitrotational motion between the first end plate lower surface and thesecond end plate upper surface.
 21. The vertebral body replacement ofclaim 16, further comprising: an adjustment mechanism between the firstand second end plates, the adjustment mechanism configured and arrangedto selectively move the first and second end plates towards and awayfrom each other.
 22. The vertebral body replacement of claim 16, furthercomprising at least one bone ingrowth hole in at least one of the firstand second end plates.
 23. The vertebral body replacement of claim 16,wherein each of the first and second end plates comprise a lateralsurface, and wherein the at least one bone ingrowth hole extends betweensaid lateral surface and said surface configured to engage against asurface of a remaining vertebral body.
 24. The vertebral bodyreplacement of claim 16, wherein the vertebral body replacement is sizedand shaped to replace one or more entire vertebral bodies of the humanspine.
 25. A vertebral body replacement for replacing at least onevertebral body between remaining upper and lower vertebral bodies, thevertebral body replacement comprising: a first end plate having an uppersurface configured to engage against a surface of the upper remainingvertebral body and at least one elongated fin on the upper surfaceconfigured to enter a slot cut in the upper remaining vertebral body; asecond end plate having a lower surface configured to engage against asurface of the lower remaining vertebral body and at least one elongatedfin on the lower surface configured to enter a slot cut in the lowerremaining vertebral body; a compliant connector section between thefirst end plate and the second end plate, the compliant connectorsection comprising a plurality of separate stackable spacers each havingat least one helical cut configured and arranged to permit limitedrotation between the first end plate and the second end plate in ananterior/posterior direction and a lateral direction, wherein thecompliant connector section is configured and arranged to limit motionto less than 10 degrees between said remaining vertebrae.
 26. Thevertebral body replacement of claim 25, wherein the upper and lowersurfaces have less than 10 percent comprising holes.
 27. The vertebralbody replacement of claim 25, further comprising one or more holes inthe first and second end plates configured to receive screws extendingthrough the plates and into the bone.